The present invention relates to an optical disk device for reproducing an optical disk, and, for example, can be suitably applied to an optical disk device capable of reproducing an optical disk comprising a plurality of recording layers.
In recent years, with optical disks of the BD (Blu-ray Disc) specification, technology for increasing the number of recording layers for increasing the recording capacity has been proposed, and an optical disk with two recording layers has been put into practical use. In order to achieve even greater capacity, it is anticipated that a multilayered optical disk with three or even four or more recording layers (hereinafter referred to as a “multilayered disk”) will be put into practical use.
Nevertheless, in the reproduction of a multilayered disk, deterioration in the reproduction quality easily occurs due to the deterioration in the reflectance of the recording layer. Thus, this problem is resolved by increasing the direct current and the high frequency superimposed current supplied to the laser diode for emitting a laser beam to the optical disk in order to obtain a favorable S/N ratio.
Meanwhile, in the case of a recordable optical disk, if the direct current and the high frequency superimposed current supplied to the laser diode are simply increased, it will not be possible to ensure so-called reproduction durability.
In response to the foregoing problem, Japanese Unexamined Patent Application Publication No. 2009-140580 discloses technology for setting optical read power in an optical disk device by gradually increasing the read power, measuring an index value representing the quality of the reproduction signal upon reproducing the optical disk at the respective read powers, and referring to the lower limit read power in which the measured index value becomes a minimum value.
Moreover, Japanese Unexamined Patent Application Publication No. 2007-172770 discloses technology in which, in an optical disk device, a jitter detector reproduces the recorded information and detects it as a reproduction signal, and a controller sets the superimposition level of the high frequency current according to the reproduction signal that was detected with the jitter detector.